PLANT PHYSIOLOGY , Vol 109, Issue 2 375-384, Copyright © 1995 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Biochemical Response of Electrical Signaling in the Reproductive System of Hibiscus Plants
J. Fromm, M. Hajirezaei and I. Wilke
Forstbotanisches Institut, Universitat Gottingen, Busgenweg 2, 37077 Gottingen, Germany (J.F.)
Stimulation of the stigma of Hibiscus flowers by pollen, wounding (heat),
or cold shock (4[deg]C) evokes electrical potential changes in the style,
which propagate toward the ovary with a speed of 1.3 to 3.5 cm s-1.
Potential changes were measured intracellularly by microelectrodes inserted
in the style. The resting potential ranged from -90 to -112 mV (n = 20) in
cells of the vascular tissue and from -184 to -220 mV (n = 22) in cells of
the pollen-transmitting tissue. The amplitude of the potential changes was
between 40 and 150 mV, depending on the kind of stimulus. Self- as well as
cross-pollination hyperpolarized the resting potential after 50 to 100 s,
followed by a series of 10 to 15 action potentials. In contrast, cooling of
the stigma caused a single action potential with a different shape and
duration, whereas wounding generated a strong depolarization of the
membrane potential with an irregular form and a lower transmission rate. To
determine the physiological function of the different signals measured in
the style, the gas exchange and metabolite concentrations were measured in
the ovary before and 10 min after stimulation of the stigma. Self- and
cross-pollination caused a transient increase of the ovarian respiration
rate by 12%, which was measured 3 to 5 min after the stigma was stimulated.
Simultaneously, the levels of ATP, ADP, and starch increased significantly.
In contrast, both cold shock and wounding of the stigma caused a
spontaneous decrease of the CO2 content in the measuring chamber, as well
as reduced metabolite concentrations in the ovary. Since the transport of
labeled auxin from the top to the base of the style lasts at least 45 min,
the influence of a chemical substance transmitted within 10 min is
unlikely. Thus, our results strongly support the view that different,
stimulus-dependent electrical signals cause specific responses of the
ovarian metabolism.
